Different Ways to Fasten Biological Indicators (BI)

Introduction to BIs

Biologicalicq_pic_micro (1) indicators (BIs), as defined by ANSI/AAMI and ISO, are test systems containing viable microorganisms providing a defined resistance to a specific sterilization process. A biological indicator provides information on whether necessary conditions were met to kill a specified number of microorganisms for a given sterilization process, providing a level of confidence in the process. Endospores, or bacterial spores, are the microorganisms primarily used in BIs. These microorganisms are considered some of the toughest ones to kill. Additionally, bacterial spores are chosen for a specific sterilization process based on their known resistance to that process. For example, Geobacillus stearothermophilus spores demonstrate a high resistance towards steam and vaporized hydrogen peroxide and are therefore used in BIs that monitor these sterilization processes.

Biological indicators, depending on the specific type, can be used for various sterilization processes using steam, hydrogen peroxide gas, ethylene oxide and more.  Several factors such as operator experience, load preparation and sterilizer condition can impact the sterilization cycle. BIs provide a direct measure of the lethality of the process and so the use of BIs to routinely monitor sterilizers provides assurance in the efficacy of the sterilization process.  BIs are typically used within process challenge devices (PCD) that are designed to represent the most challenging products routinely processed. A passing result for the BI within this defined challenge demonstrates that the sterilizer is effective in killing many highly resistant bacterial spores, providing users with a level of assurance in their sterilization process.

Fastening BIs – Pitfalls and Tips

There are many ways to fasten BIs to your thermocouples, depending upon your specific activity. For example, utilization of BIs can vary from creating new loads for an autoclave or for a steam-in-place for a Bioreactor and transfer lines.  It also depends on what type of materials are available (tie wraps, zip ties, autoclave tape, screens, etc.).  The main idea here is to secure the BI while still allowing steam penetration. In an autoclave you have virtually no chance to overly damage/lose BIs because they are usually in tubing, autoclave bags, assemblies, etc.  versus a steaming process in a transfer line.  In which case, the steam and condensate flow in the lines can damage your wet BIs and also potentially damage your BI fastener causing you to lose them in the lines. For example, fastening a BI with the improper tie wraps could melt the tie wraps to the BIs and piping.

Practical Methodology

When wrapping the BIs for an autoclave, fold the BI around the thermocouple (towards the tip of the TC) by folding the BI so it resembles a mini-burrito.   I have used autoclave tape on the BI edges to hold it to the TC and have also used tie-wraps.  Either way, ensure the tape or tie wraps aren’t too tight (twist tie wrap a few times) to rip the envelope of the BI.  Then place the BI with the TC into your load items.


When fastening the BIs for tanks/process lines, place the TC in the BI, fold it like a burrito, and then fold it in half.  Take the tie wrap (approximately a foot long) and twist it around the BI starting at the top.  With the remaining length of the tie wrap, twist it together so it secures the BI from moving.  Since this one is a bit harder to visualize, refer below for a picture.  It reminds me of a bottle rocket.  Then you can either attach it to the TC or place it in the piping beside the TC ensuring an inch or two is secured by the clamp.  This prevents the movement of the BI.

In Closing…..

Like many processes, there are multiple ways to get the job done.  If this blog saves even one BI and an Engineering/Validation person’s resultant frustration, then it was all worth it!

Written By: Frank Gatta, Senior Consultant